Marsilea batardae was recently distinguished from Marsilea strigosa, from which it differs in sporocarp size and form. All subpopulations of Portugal, previously attributed to Marsilea strigosa, belong to Marsilea batardae (Launert 1983).

Justification:Marsilea batardae is endemic to the Iberian Peninsula where it has a small area of occupancy (below 500 km²) and is subject to continuing declines in area of occupancy, quality of habitat, number of subpopulations and number of mature individuals. It is found at around 25sites and the subpopulations are considered as severely fragmented. The main threats are general destruction and degradation of standing water bodies, the modifications of hydrological networks such as the construction of dams and the embankment of streams and the degradation of water quality. Marsilea batardae is therefore assessed as Endangered.

Marsilea batardae is an endemic of the Iberian Peninsula, where it is limited to the southwestern quarter, mainly in the hydrological basins of the rivers Tejo, Sado, Guadiana and Guadalquivir.In Portugal, it occurs in the Alentejo region (Alqueva dam) and São Miguel do Pinheiro region, east of the Parque Natural do Vale do Guadania. In Spain it is found in the southwest, provinces of Badajoz, Ciudad Real, Huelva, Caceres and Córdoba (Bañares et al. 2004). Its presence is uncertain in the provinces of Toledo and Valencia (Rosselló-Graell et al. 2000).The area of occupancy is estimated to be smaller than 500 km².

Marsilea batardae presents a divided distribution area. The number of localities is close to 25. In Portugal, the number of individuals, though not precisely estimated, may be considered as low (ICN 2006). On one hand about five localities have disappeared due to the construction of the Alqueva reservoir in Portugal, on the other hand around seven new localities have been found in Spain since 2004, especially in the area of Andalucia (L. Medina pers. comm. 2010). The population for Spain has been estimated in 115,838 individuals (Bañares et al. 2004).In Spain, most of the populations extinct are from the same area (Extremadura) due to river and basin transformations for dams. Only a few populations from other areas disappeared due to others reasons. In Portugal, some of the populations are disappearing due to changes in crop areas in the Alentejo province.

The subpopulations are considered as severely fragmented as the population exchange is due to river water flow and an exchange is therefore mostly taking place downstream and linked to rainfall periods. In the past, it is suspected that the genetic exchange was due to traditional cattle movements (in Spanish "trashumancia"), when sheep move to high green areas in spring and return to low areas for the winter. This kind of cattle movement is not practised anymore.

Marsilea batardae is a perennial species growing at low altitudes, on clays and sands deposited in temporarily flooded areas (e.g. banks of streams) but also in rock fissures and in stony riverbeds. Its development is dependent on groundwater level and quality. The species prefers water that is poor in nutrients and salts but the biggest population is found in a rather eutrophic reservoir. It is probably a characteristic species of the class Littorelletea (Tüxen 1947).

Marsilea batardae, previously considered as Vulnerable in Portugal (Dray 1985, Walter and Gillett 1997), was proposed as Endangered on the basis of the reduction of area induced by the construction of the Alqueva dam (Rosselló-Graell et al. 2000). In Spain, it was considered as Critically Endangered (Dominguez Lozano 2000), and more recently as Endangered (Bañares et al. 2004, Moreno 2008).The main threats are related to the general destruction and degradation of standing water bodies, the modifications of hydrological networks, notably through the construction of dams and the embankment of streams and the degradation of water quality. All these factors lead to a reduction of the natural habitat of Marsilea batardae, and seriously threaten its long-term survival.

M. batardae is protected at European level under the Habitats Directive 92/43/CEE (annexes II andIV) and included in Appendix I of the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention).In Spain it is furthermore protected at regional level (Andalusia, Castilla-la-Mancha, Extremadura) and is included in the national Red List (EN A2ace+3ace+4ace; B2ab(i,ii,iii,iv)).In Portugal, the species is protected under decree-law n°140/99 (annexes B-II b/ e B-IV b/) and decree-law n°316/89 (Annexe I). Marsilea batardae is included in the seed bank project for the flora affected by the Alqueva dam.

The following future conservation measures are being proposed:

Control of the water quality and of the hydrological regimes of concerned streams

Monitoring of the sub-populations, notably the ones affected by the Alqueva dam (Portugal)

Evaluation of the size of the subpopulations

Study of the dynamics of the subpopulations, in relation to drainage, irrigation and other hydrological modifications